(a) Field of the Invention
The present invention relates to CNC (computer numerically controlled) machining technology, and more particularly, to off-line feed rate scheduling for reduction of machining time and enhancement of machining accuracy in CNC machining.
(b) Description of the Related Art
Research into metal machining technologies has taken on increasing importance as design and production cycles of a product become shorter in response to changing consumer demand. This is particularly true in the present-day industrial situation where a company's survival is closely linked to its ability to remain economically competitive. Modern production workers perform machining by relying upon empirical machining conditions even after a tool path is generated using CAM (computer aided manufacturing) software. Production workers depend mainly on stable machining conditions such that production time is reduced. Further, in transient cut regions such as a corner section where a tool path is encountered, machined surface errors occur severely because production workers randomly adjust a feed rate in these regions. In addition, many processes are required to remove these machined surface errors generated during NC machining.
These problems may be overcome through the systematic selection of machining conditions. Since a feed rate scheduling system gives a manufacturing machine user optimum machining conditions that take into consideration ease of machining, machining stability, and machined surface errors, it can be a useful tool in many respects (e.g., to reduce production costs and to make more various kinds of small production).
In CNC machining, although the need to optimize feed rate, which is related to productivity improvement, is becoming increasingly important, it has not yet become a common technology that can be used for the manufacture of a wide variety of products. This is a result of the fact that analysis is not definitely performed with respect to the cutting process such that it is difficult to anticipate machining results of various cutting conditions. In order to determine optimum cutting conditions for CNC machining, a process of trial and error is undertaken. Since it is difficult to format this knowledge for input to a database, a new production worker must start anew until he or she becomes familiar with the processes.
CAM software companies are introducing feed rate optimization methods to improve their competitiveness. However, feed rate optimization methods used in most CAM software available today uniformly maintain an MRR (material removal rate) in consideration of a geometric relation between a workpiece and a tool. However, in methods utilizing MRR, it is not possible to put precision adjustment of a cutting force and a cutting force coefficient in database form. Since the intensity of the cutting force may vary greatly according to changes in spindle speed even with the same MRR, such methods result in reducing competitiveness. Accordingly, a feed rate scheduling method that is based on a cutting force model is needed. If accurate, the cutting force model would be able to be effectively applied to feed rate scheduling.